1. Field of the Invention
This invention relates to portable electric power tools employing an endless work engaging belt such as a portable electric belt sander and, more particularly, to a novel and improved construction for influencing an endless sanding belt or the like to track substantially centrally on the belt supporting and driving rollers.
2. Description of the Prior Art
Most belt tracking mechanisms for commercially available portable belt sanders have employed a support for the belt idler roller which sustains the idler roller axis in the same plane as the axis of the drive roller but provides a pivotal support for the idler axis perpendicular to the common plane so that the idler axis may be swung out of parallelism with the axis of the drive roller. Self correcting means, where present in belt tracking mechanisms of this type, require edge contact with the abrasive belt by feed-back linkages which are wear prone and complicated mechanisms. The Murschel U.S. Pat. No. 3,094,819, June 25, 1963, and that of Rameckers et al U.S. Pat. No. 4,177,609, Dec. 11, 1979, are representative of such conventional belt centering constructions for portable belt sanders.
In abrading machinery not of a portable nature, tracking of an abrasive coated belt has been controlled by providing a support for a belt idler roller in a plane parallel to the axis of the drive roller but providing a pivotal support for the idler roller perpendicular to the plane containing the idler roller axis and about which the idler roller axis may be turned to impart a twist in the belt. The Przgocki U.S. Pat. No. 3,665,650, May 30, 1972, and that of Habeck et al U.S. Pat. No. 3,971,166, July 27, 1976, are representative of such emplaced abrading or sanding machinery. No portable belt sanders are known showing this type of belt tracking mechanism with self adjusting capability. The patented emplaced sanding machinery referenced above disclose complicated and space consuming belt sensing servomechanisms for self correcting belt centering, which mechanisms are ill adapted for use in portable belt sanders.